As discussed with nenolod, this is one of the main goals of 3.4 as far as I'm concerned:

UnrealIRCd currently has a lot of modularity to offer, yet many (almost all) of the channel modes are built in the core. That's a shame, as it defeats the modular approach.

We should move as many modes as possible to modules.
Some are really easy and require almost no effort.
For others you'll have to introduce some new hook types, that too is perfectly doable.
And yes, a few, are too hard to modularize.

Side note: RFC1459 modes don't have to be in modules (per se), it's more about the rest.

I already started on this once in 3.3 (that work isn't useable anymore, so has to be redone) and it's quite possible, even for more complex modes.